The present invention relates to an arrangement for closing off sections of channels in a hot-channel runner.
It is a known fact that in devices that are used for hot-channel injection moulding, cylindrical plugs can be used in the corner area of a runner channel; these are used to close off the ends of the channel and/or to connect sections of the channel that are angled as deflectors to tapered bores so as to produce a pressure-tight fit. As an example, according to EP 0 226 798 A1, plugs are inserted coaxially at the ends of a main runner in order to connect them to a diverter with a tapered hole. This continues in the plug with an angled bore that leads to an outlet opening of the runner. A constriction is formed at the bevel of the bore and, in principle, this presents resistance to the flow; if plastified injection material adheres at this point, this makes cleaning extremely difficult or impossible, so that the plug as a whole has to be replaced. These plugs are fixed in the runner by being soldered in position, for which reason mechanical cleaning of the channels is not possible without considerable effort.
A similar arrangement is described in DE 32 11 342 A1. In this arrangement, a cone is inserted into each widened opening of a runner cross channel, and this can be closed off so as to be pressure tight by means of a catch that is inclined at one end and secured in the runner by means of a screw. This means that blind corners in which residual material can collect are unavoidable, and this will eventually disrupt operation or degrade the quality of the product and will, in any case, render cleaning more difficult.
Improved arrangements are described in EP 0 523 549 A2, EP 0 630 733 B1, and EP 0 845 345 A1; these incorporate conical steel inserts that have deflector bores and are secured to the runner by truss-head screws, by being pressed into place by adjuster screws with internal tapers, or are covered by studs.
Even though connections of this kind can operate under extremely high injection pressures, production costs are relatively high and it is not always simple to achieve a precise installation of the tapered inserts. It can be difficult, or even impossible, to achieve exact positional congruence between the bore in the cone and the bore in the runner. In addition, the position of the tapered bore in the runner bore depends on application pressure. This relationship is made even more problematic, the thinner the taper. It is impossible to avoid having blind corners and covered areas in the flow within which injection material can be deposited.
It is an important objective of the present invention to improve this situation and to develop a new type of arrangement which will either avoid the disadvantages described above, as well as other disadvantages found in the prior art, or else eliminate them by simple means. It is intended to satisfy the severe demands imposed by high-speed injection moulding operation and also permit rapid colour changes. In addition, a further aim of the present invention is to describe a configuration of the connection arrangement such that the manufacture of balanced runners is made more simple. The means that are used to do this are intended to provide for cost-effective production and ensure convenient installation and removal.
In accordance with the invention, in an arrangement for closing off channel sections in a hot-channel runner that has at least one channel that can be charged with a plastified mass and which can be closed of so as to be pressure-tight by plugs that are secured to tile runner so as to be removable, the present invention makes provision such that the plug can be secured in the runner so as to subtend an acute angle with the axis of the channel. This plug has a face surface that can be pressed against a closed annular surface, which encloses an opening in the channel or defines this, in such a way as to be pressure tight. It is thus possible to achieve a fully effective seal that can withstand extremely high pressures, e.g., in the range above 2 kbar, without having to accept blind corners. The plugs form releasable stoppers that permit mechanical cleaning. Thanks to their inclined position, they can be installed and removed rapidly, so that the operations required for a change of material or colour can be completed in an extremely short time.
In accordance with another feature of the invention, the face surface of the plug is configured as a closed sealing edge on a pressure piece that is guided along its axis. This feature results in a precisely shaped seal on the annular surface. Imprecise alignment or shifting of the annular and face surfaces are thus avoided from the very outset. The pressure piece can be moved in a particularly simple manner if the plug incorporates a screw body, to or in which a tool can be fitted.
In accordance with yet another feature of the invention, the plug may be formed in two parts, in that a separate pressure piece precedes a screw head. It is an additional feature of the invention that this pressure piece may be guided precisely in an inclined bore that opens out into the area of the channel in the runner that is to be sealed off. Because of the close fit of the face surface of the plug on the annular surface, minor angular deviations or even a small offset of the separated screw body will not affect the seal that is achieved. The inclined bore is best made as a stepped bore, with a threaded section to accommodate the screw head being adjacent to an outside section of somewhat greater diameter, this being followed inside by a cylindrical and even narrower section within which the pressure piece of the plug fits very closely.
In accordance with another aspect of the invention, the face surface of the plug can be flat, at least in part, namely, on the sealing edge, so that an immediate, tight form fit with the annular surface is ensured. The face surface of the plug may be curved, which is to say that, in particular, it projects partially from the plane of the seal within the sealing edge. Such curvature may be in the form of a spherical segment, the maximal radial extent of whichxe2x80x94as related to the axis of the plugxe2x80x94is defined by the smallest radius of the sealing edge.
It is still another aspect of the invention that the curvature of the face surface may be concave. Thus, it forms a recess by which it is possible to achieve a precise and improved shape at a corner or elbow of the channel section without the need to prevent rotation of the plug or of the pressure piece. In particular, in this way it is also possible to achieve a continuous transition to a branch channel so that an even or continuous cross section is formed; an associated nozzle with an identical channel width can be installed adjacent to this.
Yet another feature of the invention offers still other advantages in providing a convex, in particular slightly spherical, curvature on the face surfaces and/or on the upper side of the pressure piece that is proximate to the screw head. In addition, if there is an angular deviation from the axis of the plug, in addition to the central pressure, there will be radial force components that act outward, and these can further improve the seal.
It is another aspect of the invention that the pressure piece may have a threaded hole that is arranged, in particular, centrally, into which, once the screw head has been removed, an extraction screw can fit in order to facilitate convenient removal of the pressure piece from the inclined bore in the runner, e.g., for cleaning purposes.
It is an advantage if, in accordance with an additional feature of the invention, the annular surface is arranged at a corner or elbow, where the channel makes a transition to a branch or outlet opening of the runner, particularly for injecting plastic into a nozzle that is arranged on the runner. According to still another feature, on the outside the annular surface is delimited in a circle, whereas the inside shape can be oval, for instance at an elbow or bend in the channel. A tool that is inserted obliquely into the runner, such as a milling head, can generate the annular surface in this corner area. Its size and inside shape will be determined by the angle subtended with the axis of the channel as well, as by the penetration depth achieved by the tool. In another configuration, the annular surface is formed, for example, as a ground and polished surface such that it defines a plane that is perpendicular to the angle. Because of this, the face surface of the plug that is to be sealed is exactly parallel to said surface, whereby a close fit against the annular surface will be ensured in every case.
It is still another aspect of the invention that selected sections can be closed off by pairs of plugs that are associated with each other on a runner channel with a series of branches. Thus, in a particularly rational manner, it is possible to provide a through channel in the runner from which branch nozzles that are arranged symmetrically, e.g.. in pairs, can be supplied with injection plastic in a precisely balanced arrangement. From the design standpoint, it is of advantage if, according to yet another aspect, there are annular surfaces that are inclined in the opposite sense to each other at the end of the channel, in which the correspondingly inclined plugs can be installed.
Generally speaking, for both the installation and for the effect of the plug it is useful, according to one feature of the invention, to arrange the plug at an angle to the axis of the channel that is in the range from 30xc2x0 to 45xc2x0, preferably 40xc2x0 to 45xc2x0. Such an inclined position provides not only good accessibility but also ensures a large periphery of the opening""s annular surface on the particular canal section or area. One thereby avoids excessive mechanical loads and excessive pressure per unit area on the channel or at an elbow or corner. In addition, it permits a really exact form fit on a relatively extended annular surface. There are no areas shielded from the flow of material in the outlet to the nozzle; rather, this area can be completely flushed because, in the normal course of events, material is often deposited directly behind the diversion point, and this is thermally damaged during operation.
According to an additional feature of the invention, a plug can be fixed in position, e.g., by means of a safety pin that can be so screwed into or inserted into the runner, transversely to the axis of the channel, or transversely to the axis of the plug, that the plug is wedged into position.
Additional features, details, and advantages of the present invention are set out in the claims and in the following description, which is based on embodiments shown in the drawings appended hereto. These drawings show the following: